' 


CONFIDENTIAL— FOR  OFFICIAL  USE  ONLY 


NOTES  ON 

ANTI-AIRCRAFT  GUNS 


Compiled  at  the  Army  War  College 
From  the  Latest  Available  Information 


APRIL,  1917 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 
1917 


WAR  DEPARTMENT. 

DOCUMENT  No.  5 7"). 
Office  of  The  Adjutant  General, 


WAR  DEPARTMENT, 

WASHINGTON,  April  28,  1917. 

The  following  Notes  on  Anti-Aircraft  Guns  are  published  for 
the  information  of  all  concerned. 
[2582933  A— A.  G.  O.] 

BY  ORDEK  OF  THE  SECRETARY  OF   AV.\K  : 

H.  L.  SCOTT, 

Major  General,  Chief  of  Xtaff. 
OFFICIAL  : 

H.  P.  MCCAIN, 

The  Adjutant  General. 

3 


ITALY. 

The  Italians  use  the  75  mm.  (3-inch)  Deport  gun  for  anti- 
aircraft service.  It  has  a  maximum  elevation  of  85°,  and  fires 
21  shots  a  minute.  Shrapnel  is  considered  inefficient;  the  high 
explosive  shells,  which  are  much  preferred,  carry  either  a  time 
or  a  detonating  fuse.  The  incendiary  shell,  used  with  a  time 
fuse,  throws  out,  upon  exploding,  a  number  of  small  halls  con- 
taining a  very  efficient  burning  liquid.  Six-gun  batteries  have 
been  substituted  for  the  formerly  adopted  two-gun  battery. 

The  Italian  Army  in  September,  1916,  had  16  batteries  (4 
guns  to  a  battery)  of  anti-aircraft  guns  mounted  on  automo- 
biles. The  gun,  made  by  Ansaldo  &  Co.,  is  of  102  mm.  caliber. 
It  is  reported  that  the  number  of  these  guns  has  since  been  in- 
creased. 

Illustration  No.  1  shows  an  Italian  flat  car  armed  with  two 
anti-aircraft  guns.  The  three  heavy  brackets  (B)  are  used  to 
brace  the  car  against  recoil  when  the  guns  are  fired.  Before 
firing  they  are  swung  out  at  right  angles  to  the  car  on  the  side 
away  from  the  gun  direction  and  a  heavy,  threaded,  steel  rod 
is  screwed  down  through  the  band  (a)  until  its  lower  end 
presses  firmly  against  a  truncated  pyramidal  block  (b),  which 
is  placed  on  the  ground  to  receive  it.  To  facilitate  rapid  ad- 
justment a  detachable  wheel  (c)  is  attached  to  the  top  of  the 
screw  rod.  It  is  believed  that  these  braces  are  used  only  in  the 
case  of  firing  the  heavier  (6-inch)  guns. 

FRANCE. 

The  main  reliance  of  the  French  for  defense  against  aircraft 
is  their  75  mm.  gun,  model  of  1897,  which  fires  25  shots  a  minute 
and  has  a  recoil  mechanism  so  perfect  that  it  can  be  fired  con- 
tinuously without  relaying.  This  gun  is  shown  in  illustrations 
2,  3,  4,  and  5,  but  the  reports  show  that  the  mountings  have 
been  modified.  For  anti-aircraft  work  this  gun  has  been 
mounted  in  three  different  ways,  as  follows : 

5 


6  NOTES  ON  ANTI-AIRCRAFT  GUNS. 

1.  On  an  improvised  fixed  mount  for  the  ordinary  Hold  car- 
riage. The  wheels  of  the  carriage  rest  on  a  circular  plat  Turin 
with  a  strong  vertical  pivot  in  the  center.  To  obtain  the  high 
elevation  necessary,  the  trail  is  sunk  in  a  circular  pit  32  inches 
below  the  level  of  the  wheels.  In  order  that  the  trail  may  not 
be  driven  into  the  ground,  there  is  attached  to  it  a  chock,  fitted 
with  a  traversing  roller  resting  in  the  pit  on  a  wooden  travers- 
ing circle.  To  the  pivot  supporting  the  carriage  is  fixed  a  pivot 
collar  which  turns  freely  and  carries  four  arms.  To  each  of  the 
two  longitudinal  arms  is  attached  a  tie-rod  bolted  at  the  other 


No.  2.— FRENCH  75  MM.  FIELD  GUN  ON  FIXED  MOUNTING  FOR  AERIAL  DEFENSE 

OF  PARIS. 

end  to  the  trail  chock.  These  lie-rods  resist  the  recoil  of  the 
carriage.  To  each  of  the  two  lateral  arms  is  attached  an  elastic 
tie-rod  fitted  at  the  upper  end  with  a  bronze  strap  holding  the 
axle  of  the  carriage.  The  elastic  tie-rods  are  equipped  with 
spiral  springs  which  steady  the  carriage.  A  pointing  mechan- 
ism attached  to  the  left-hand  side  of  the  trail  includes  a  trav- 
ersing wheel  which  actuates,  by  means  of  transmitting  gears. 
the  traversing  chock  roller. 

The  field  of  fire  is  360°. 

2.  On  a  metallic  demountable  platform  for  the  fixed  defense 
of  towns  or  with  a  modified  substructure  for  use  in  the  field. 
In  the  first  case  a  concrete  pit  is  prepared  I  meters  in  diameter 
and  1  meter  deep.  At  the  center  of  the  pit  is  bolted  a  base  plate 
with  a  socket  in  which  turns  the  vertical  pivot  supporting  the 
mounting. 


NOTES  ON  ANTI-AIRCKAFT  GUNS.  7 

The  framework  of  this  mounting  is  composed  of  two  trian- 
gular trusses  of  riveted  U  beams  iu  vertical  planes,  making  an 
angle  with  each  other  of  30°  and  of  two  central  brackets.  To 
support  the  personnel,  there  rests  on  the  trusses  and  the  central 
brackets  a  flooring  which  is  open  between  the  brackets  to  pro- 
vide space  for  the  trail  of  the  piece  and  for  the  winch  used  for 
pointing  in  elevation.  The  uprights  of  the  two  trusses  are 
suitably  cross  braced,  the  lower  brace  being  fixed  to  the  pivot 


No.  3.— IMPROVISED  ANTI-AIRCRAFT  MOUNT  FOR  FRENCH  75  MM.  FIELD  GUN. 

support.  At  the  top  these  uprights  are  fitted  with  trunnion 
beds  designed  to  receive  the  axle  of  the  gun  carriage  from 
which  the  wheels,  wheel  brakes,  and  shields  have  been  removed. 
The  trail  of  the  carriage  is  supported  by  a  steel  cable  wound  on 
the  winch,  which  is  operated  by  means  of  an  elevating  mechan- 
ism on  the  left-hand  platform. 

To  facilitate  the  elevation  and  depression  of  the  gun  the  car- 
riage has  a  counterweight  consisting  of  a  cast-iron  ball  placed 
under  the  gun  and  supported  from  the  axle  of  the  carriage  by  a 
steel  wire  cable  passing  through  a  hole  in  the  ball  and  held  out 


8  NOTES  ON  ANTI-AIRCRAFT  GUNS. 

by  means  of  a  wooden  outrigger,  one  end  of  which  is  placed 
in  a  recess  of  the  counterweight  while  the  other  end  is  secured 
to  the  trail. 

Each  truss  is  fitted  at  the  rear  and  under  the  flooring  with 
a  large  cast-iron  traversing  roller,  which  travels  on  an  iron 
traversing  circle  set  in  the  exterior  coping  of  the  pit.  By  turn- 
ing a  handwheel  connected  to  the  right-hand  roller,  the  entire 
framework  can  be  made  to  rotate  around  the  pivot. 

Pointing  in  direction  and  pointing  in  elevation  are  distinct  oper- 
ations, done  by  separate  men.  For  large  movements  in  direction 
the  mounting  is  pushed  around  by  hand.  The  smaller  move- 
ments are  given  by  the  before-mentioned  traversing  handwheel. 
The  cannoneer  pointing  for  direction  is  on  a  seat  attached  to 
the  right-hand  truss.  In  front  of  him,  near  the  traversing 
handwheel  on  a  sight  bracket  placed  at  the  top  of  a  column 
fastened  to  the  truss,  is  the  sight  for  direction,  consisting  of  an 
ordinary  telescopic  sight  provided  with  a  deflection  scale.  The 
section  commander  computes  the  deflection  from  the  travel  of 
the  target  during  the  time  of  flight,  drift,  and  wind.  The  can- 
noneer operating  the  sight  is  given  the  deflection,  sets  it  off, 
traverses  the  carriage  until  the  vertical  cross  hair  is  on  the 
target,  and  then  keeps  the  sight  on  the  target. 

Pointing  in  elevation  is  effected  either  by  means  of  the  hand- 
wheel  operating  the  winch  which  revolves  the  entire  carriage 
around  its  axle  or  by  means  of  the  elevating  handwheel  of  the 
carriage  which  turns  the  gun  on  its  cradle.  Both  handwheols 
are  within  reach  of  the  cannoneer  pointing  for  elevation,  who 
stands  on  the  left-hand  platform.  Elevations  from  12°  to  85° 
can  be  obtained. 

The  sight  for  elevation  is  an  ordinary  telescopic  sight,  the 
mounting  of  which  is  in  gear  with  the  range  dial.  The  can- 
noneer at  this  siglit  keeps  the  horizontal  wire  of  his  sight  on 
the  target  at  all  times  by  elevating  or  depressing  the  gun  by 
means  of  the  elevating  handwheels.  The  range  dial,  about  a 
foot  to  the  left,  is  operated  by  another  cannoneer.  It  consists 
of  a  small  brass- disk  on  which  are  curves  corresponding  to  the 
different  ranges.  By  moving  the  pointer  along  these  curves  to 
the  range  given,  the  necessary  elevation  is  transmitted  to  the 
telescopic  sight  for  elevation.  Thus,  when  a  change  of  range  is 
announced,  the  gunner  being  already  on  the  target,  the  can- 
noneer moves  the  pointer  to  the  new  range:  this  throws  the 
gunner  off  the  target,  and  he  at  once  relays  the  piece. 


NOTES  ON  ANTI-AIRCRAFT  GUNS.  9 

The  detachment  consists  of  a  chief  of  section  and  eight  can- 
noneers viz,  a  pointer  in  elevation,  a  pointer  in  direction,  a  firer, 
a  loader,  a  fuse  setter,  and  three  ammunition  carriers. 

For  use  in  the  field  the  substructure  of  this  platform  mount 
is  simplified.  The  shape  of  the  pit  is  that  of  a  truncated  cone ; 
it  is  dug  1  meter  deep,  1.8  meters  in  diameter  at  the  bottom, 
and  4  meters  in  diameter  at  the  top.  A  small  parapet  about  2 
meters  thick  around  the  rim  is  formed  of  the  excavated  earth. 
The  pivot  socket  is  bolted  to  a  bolster  consisting  of  two  layers 


No.  4.— ANTI-AIRCRAFT  GUN  ON  AUTOMOBILE. 

of  wooden  joists  bolted  together,  and  is  centered  in  the  traverse 
circle  by  8  iron  tie  rods.  The  iron  traverse  circle  is  bolted  to  12 
blocks  of  wood. 

For  transportation  it  is  taken  down  in  four  parts,  which  can 
be  carried  in  two  wagons. 

In  mounting  and  dismounting  the  gun  and  carriage  an  as- 
sembling shears  is  used.  The  time  taken  is  as  follows :  To  dig 
ditch,  1£  hours ;  to  mount  platform,  \  hour ;  to  mount  gun,  5 
minutes ;  to  dismount  the  whole,  35  minutes. 

3.  On  an  automobile.  To  prepare  for  action  the  chassis  is 
supported  by  four  jack  screws.  In  addition  two  side  supports 
are  lowered  to  the  ground,  to  prevent  overturning.  The  car- 
riage permits  angles  of  elevation  from  0°  to  70°.  The  hori- 

96836°— 17 2 


10 


NOTES  ON  ANTI-AIRCRAFT   GUNS. 


y.ontal  lit-ld  of  lire  is  limited  to  240°,  as  the  breach  can  not  pass 
certain  positions. 

Until  recently  time  shrapnel  was  used  almost  exclusively,  but 
now  the  French  are  using  high-explosive  shells  with  time  fuses. 
When  shrapnel  is  used  the  entire  percussion  element  is  removed, 
for  the  protection  of  friendly  troops,  in  case  the  time  element 
of  the  fuse  does  not  function.  There  is  also  a  smoke-producing 
shell,  filled  with  fuse  composition,  and  the  ogive  is  pierced  with 
holes.  It  is  primed  with  a  time  fuse,  which  communicates 


No.  5— FRENCH  OFFICIAL  PHOTOGRAPH  FROM  THE  SOMME. 

flames  to  the  interior  charge,  which  escapes  through  the  holes 
in  the  ogive.  Thus  it  is  possible  to  follow  the  projectile  through 
its  trajectory,  which  is  of  great  assistance  in  anti-aircraft  gun- 
nery. 

In  addition  to  the  75  mm.  gun,  it  is  known  that  the  French 
are  using  for  aerial  defense  the  105  mm.  gun,  also  the  37  nun. 
rapid-fire  naval  gun.  In  Paris  some  37  mm.  guns  are  on  tripods, 
while  one  is  in  a  cupola.  No  further  information  is  on  hand. 

According  to  the  latest  information  received  on  anti-aircraft 
guns  on  automobile  mounts,  the  75  mm.  gun  is  used  for  firing  a 
shrapnel  weighing  7.4  kilograms  (16J  pounds)  with  a  muzzle 
velocity  of  525  meters  per  second  (1,722  feet  per  second)  and 


NOTES  ON  ANTI-AIRCRAFT  GUNS. 


11 


a  high-explosive  shell  weighing  5.315  kilograms  (111  pounds) 
with  a  muzzle  velocity  of  584  meters  per  second  (1,815  feet  per 
second).  This  fire  appearing  insufficient  against  aeroplanes 
flying  at  great  altitudes  there  is  now  under  consideration  a 
90  mm.  anti-aircraft  gun.  with  a  muzzle  velocity  of  approxi- 
mately 750  meters  per  second  (2,460  feet  per  second)  for  a 
shrapnel  weighing  11  kilograms  (24  pounds).  • 

The  use  of  the  75  mm.  gun  with  a  high  muzzle  velocity  ap- 
pears to  be  preferable  to  that  of  the  105  mm.  with  a  reduced 
muzzle  velocity. 

GERMANY. 

The  German  have  used  for  anti-aircraft  work  numerous  dif- 
ferent types  of  guns,  generally  ranging  in  caliber  from  50  mm. 


No.  6.— EHRHARDT  65  MM.  ANTI-BALLOON  GUN  L-35. 

to  105  mm.,  though  calibers  as  low  as  37  mm.  and  as  high  as 
120  mm.  have  been  reported.     Some  of  these  guns  had  already 


12  NOTES  ON  ANTI-AIRCRAFT  GUNS. 

been  developed  before  the  war  began,  while  others  have  since 
been  brought  out,  the  tendency  being  toward  a  constant  in- 
crease in  caliber,  range,  and  muzzle  velocity.  The  incomplete 
and  sometimes  more  or  less  conflicting  reports  concerning  some 
of  these  guns  make  it  difficult  to  coordinate  the  data  on  hand, 
which  for  some  guns  are  very  meager. 

The  earliest  German  antiaircraft  gun  of  which  we  have  any 
information  is  the  65  mui.  (2.56-inch)  Ehrhardt  anti-balloon 
gun  developed  several  years  before  the  war.  This  gun  is  35 
calibers  long,  fires  with  a  muzzle  velocity  of  2,000  feet  per  sec- 


No.  7.— EHRHARDT  65  MM.  ANTI-BALLOON  GUN. 

ond,  a  9.4-pound  projectile,  at  a  maximum  elevation  of  75°  to  a 
maximum  height  of  26,000  feet.  The  maximum  range  for  time 
fuse  is  5,960  yards,  and  for  percussion  fuse  7,760  yards.  The 
gun  has  quick  and  slow  movement  in  azimuth  and  all-around 
fire.  It  is  mounted  on  a  center-pivot  cradle  carriage  on  an  au- 
tomobile truck  with  broad  wheels  weighing  about  7  tons  (illus- 
trations 6,  7,  8,  and  9).  Weight  of  gun  and  carriage  is  1,900 
pounds.  With  a  level  and  two  handwheels  the  upper  carriage 
can  be  quickly  leveled.  The  automobile  has  a  wide  gun  plat- 
form with  seats  for  the  crew,  ammunition  chests  for  130 
rounds,  and  fuel  tanks  holding  sufficient  for  18  hours.  In  the 
firing  position  this  platform  is  widened  by  dropping  hack  its 
sides  and  is  supported  off  the  wheels  by  iron  props  resting  on 
a  broad  metal  base.  The  average  speed  is  50  kilometers  (31 


No.  S.-EHRHARDT  65  MM.  ANTI-BALLOON  GUN. 


No.  9.— EHRHARDT  65  MM.  ANTI-BALLOON  GUN. 


13 


14  NOTES   ON  ANTI-AIRCRAFT  GUNS. 

miles)  an  hour.  In  order  to  secure  the  necessary  rapidity  of 
fire,  the  breech  mechanism  has  been  provided  with  an  appa- 
ratus for  automatically  opening  and  closing  the  wedge-shaped 
breechblock.  A  noteworthy  feature  of  the  gun  is  the  automatic 
sight,  which  is  so  constructed  that  it  is  only  necessary  to  set 
off  the  actual  range  in  a  straight  line  to  the  target  whatever 
its  altitude,  found  by  means  of  a  telemeter,  and  to  bring  the 
target  on  the  cross  hairs.  The  line  of  sight  is  capable  of  two 
movements,  one  which  sets  off  the  necessary  angle  between  the 


NO.   10.— KRUPP  71    MM.    L-30  ANTI-BALLOON  GUN. 


axis  of  the  bore  and  the  line  of  sight  when  the  target  is  in  the 
horizontal  and  the  other  which  corrects  for  the  altitude  of  the 
target  by  automatically  decreasing  this  angle  to  a  theoretical 
zero  at  the  zenith.  There  is  also  an  automatic  fuse  time  indi- 
cator. This  is  a  brass  plate  with  curves  and  a  movable  arm 
fixed  in  the  trunnion  opposite  the  sight.  It  is  only  necessary 
to  set  off  the  given  range  and  lay  the  piece  on  the  target,  then 
the  proper  time  can  be  read. 

Another  anti-aircraft  gun  developed  by  the  Germans  some 
years  before  the  war  is  the  71  mm.  (2.8-inch)  Krupp  anti-balloon 
gun  (illustrations  10  and  11),  tiring  '20  to  !!">  shots  per  minute. 


NOTES  ON  ANTI-AIRCRAFT  GUNS. 


15 


This  gun  is  30  calibers  long,  fires  with  a  muzzle  velocity  of 
2.130  feet  per  second  an  11-pound  shell  at  a  maximum  elevation 
of  75°  at  a  maximum  height  of  21,300  feet.  Traverse,  360°.  This 
gun  is  a  barrel-recoil  gun  on  a  center-pivot  carriage,  mounted  on 
an  automobile  which  can  also  be  armored.  Weight  of  auto- 
mobile without  gun,  7,180  pounds ;  with  gun,  about  9,900  pounds ; 
with  armor  and  ammunition  chest  (carrying  122  rounds),  about 
in.400  pounds.  Mean  speed,  28  miles  an  hour.  The  gun  has 
an  automatic  horizontal  crank  closure,  rear  trunnions  and 


NO.  11.— KRUPP  71   MM.   L-30  ANTI-BALLOON  GUN. 

spring  compensator,  liquid  brake,  toothed-arc  laying  apparatus, 
and  traversing  apparatus  which  can  be  thrown  out  of  gear  for 
rapid  movement. 

It  is  also  known  that  the  Germans  had  before  the  war  de- 
veloped a  105  mm.  (4.1-inch)  anti-aircraft  gun  on  center-pintle 
mount  for  fixed  emplacements,  with  full  automatic  breech  mech- 
anism. Further  details,  however,  are  lacking. 

A  small-caliber  anti-aircraft  gun  of  high  initial  velocity  was, 
according  to  one  report,  brought  out  by  Krupp  during  the  sum- 
mer of  1915.  This  gun  has  a  caliber  of  53  mm.  (2.09  inches) 
and  a  range  of  between  4,000  and  5,000  meters  (13,120  feet  and 
16,400  feet).  The  initial  range  for  firing  being  given  the  gun 
sights  increase  in  range  automatically  50  meters  (164  feet),  so 


16  NOTES  ON  ANTI-AIRCRAFT  GUNS. 

that  the  shells  explode  in  series  50  meters  apart.  Three  guns  are 
usually  placed  in  position  together,  and  a  zone  of  lire  is  thus 
established  and  maintained  around  the  hostile  aircraft.  Several 
aeroplanes  were  brought  down  during  that  summer  by  this  .mm. 
No  further  data  are  available. 

One  report  made  during  the  summer  of  1915  gives  some  infor- 
mation about  the  firing  of  a  77  mm.  (3.03-inch)  Krupp  semi- 
automatic gun  of  about  35  calibers,  mounted  on  a  pedestal 
base  upon  a  motor  truck.  The  range  finder,  which  was  mounted 
on  a  tripod  on  the  ground  near  the  truck,  was  between  1J  and  2 
meters  long,  and  was  of  coincidence  type,  with  internal  and 
external  readings.  On  the  pedestal  mount  was  a  level,  so  that 
the  mount  could  be  leveled  before  firing.  The  sight  consist .et I 
of  a  telescope  with  two  eyepieces,  one  of  low  and  one  of  high 
power,  so  close  together  that  the  eye  could  change  readily  from 
one  to  the  other.  In  each  eyepiece  appeared  a  triangle,  point  up. 
The  gun  pointer  brought  the  aeroplane  within  the  triangle  of 
the  lower-power  eyepiece,  which  was  used  as  a  finder,  and  then, 
shifting  his  eye  to  the  high-power  lens,  he  brought  the  aeroplane 
on  the  point  of  the  triangle.  The  gun  crew  consisted  of  three 
men,  one  man  to  aim,  one  to  load,  and  a  third  to  bring  the 
ammunition  from  the  rack  and  adjust  the  fuses^  Two  officers 
were  also  present,  one  of  whom  managed  the  range  finder,  while 
the  other  gave  the  firing  directions.  Eighty-one  shots  at  a 
French  aeroplane  at  ranges  increasing  from  3,600  to  7,100 
meters  were  witnessed.  All  shots  were  fired  in  groups,  first  of 
three  and  then  of  six  shots.  The  mounts  were  clamped  during 
the  firing  of  each  group.  The  interval  between  shots  was  2>. 
seconds;  the  interval  between  groups  varied,  as  each  group  was 
allowed  to  burst  before  the  order  to  fire  the  next  group  was 
given.  The  shells  burst  with  a  thick  white  smoke.  The  powder 
used  in  the  gun  was  absolutely  smokeless,  thus  giving  no  clue 
to  the  location  of  the  gun.  The  aeroplane  was  not  hit. 

A  year  later,  namely,  during  the  summer  of  1916,  a  few  data 
were  received  concerning  an  anti-aircraft  coast  battery  of  four 
88-millimeter  (3.46-inch)  guns  with  semiautomatic  breech 
mechanism  on  shielded  pedestal  mounts  admitting  of  a  maxi- 
mum elevation  of  75°.  The  guns  were  located  at  the  corners  of 
a  square  having  a  diagonal  of  about  100  meters.  At  the  center 
of  this  square  was  the  battery  commander's  station  with  self- 
contained  horizontal  base  range-finding  instrument,  telephone 
connection  with'  central  to  receive  early  notice  of  approaching 


NOTES  ON  ANTI-AIRCRAFT  GUNS.  17 

hostile  aircraft,  and  megaphone  for  giving  verbal  orders  to  the 
gun  crews. 

According  to  a  report  submitted  late  in  1916,  the  Germans 
were  then  using  four  guns  for  anti-aircraft  work,  which,  in  the 
chronological  order  of  their  adoption  by  the  Germany  Army, 
were  stated  to  be : 

1.  A  50-millimeter  (1.96-inch)  Ehrhardt  gun  30  calibers  long, 
firing  a  1.25  kilogram  (2.75  pounds)  high-explosive  shell  with 
a  muzzle  velocity  of  572  meters  per  second  .( 1.877  feet  per  >e<-- 
ond).  Sometimes  a  2.4-kilogram  (3.08  pounds)  shrapnel  shell 
is  used.  The  maximum  elevation  is  70°.  This  gun,  on  a  cen- 
tral pivot  gun  carriage  with  cradle,  is  mounted  over  the  center 
of  gravity  of  an  armored  car.  The  cradle  contains  a  hydraulic 
brake  and  a  spring  recuperator.  The  sighting  apparatus  in- 
cludes a  muzzle  sight  and  a  mobile  breech  sight.  The  gun  is 
pointed  by  means  of  a  butt  against  the  shoulder  of  the  gunner. 
For  this  gun  there  are  two  models  of  motor  car,  differing  only 
in  their  armor  plating.  The  heavy  model  (plate  of  7-millimeter 
nickel  steel)  can  do  48  kilometers  (30  miles)  an  hour  on  level 
ground  and  can  climb  gradients  of  22°.  The  light  model  (4-mil- 
limeter nickel  steel  plate)  can  exceed  60  kilometers  (37  miles) 
an  hour.  The  latter  car  has  a  total  weight  of  3,200  kilograms 
(7,057  pounds)  when  carrying  five  men  and  material  for  100 
shots  in  the  munition  case  at  the  back  which  also  serves  as  a 
seat. 

'2.  A  65-millimeter  (2.56-inch)  Krupp  gun  35  calibers  long, 
temporarily  mounted  on  a  4-ton  motor  truck.  No  further  de- 
tails given. 

3.  A   75-millimeter    (2.95-inch)    Krupp  gun.   35   calibers  long 
(illustration  12).     This  gun  has  a  muzzle  energy  of  110  meter 
tons,  corresponding  to  a  5.5-kilogram  projectile,  and  an  initial 
velocity  of  025  meters.     With  an  elevation  of  75°  it  can  attain 
a  maximum  height  of  6.300  meters   (20.670  feet).     Since  Janu- 
ary, 1915,  it  is  mounted  on  a  specially  constructed  motor  truck 
with  solid  tires  front  and  rear  and  weighing  3.920  kilograms 
(8,640  pounds).     The  motor  develops  about  75  horsepower  and 
on  a  good  track  has  developed  a  speed  of  58  kilometers   (36 
miles)  an  hour. 

4.  A  105-millimeter  Krupp  gun,  35  calibers  in  length    (illus- 
tration 13).     This  is  the  last  gun  developed.     This  special  105- 
millimeter  gun  fires  an  18-kilogram  shell  with  a  muzzle  velocity 
of  700  meters  per  second    (2.300  feet  per  second)    and  at  the 
maximum  elevation  of  75°   reaches  a  height  of  11,400  meters 


18 


NOTES  ON  ANTI-AIRCRAFT  GUNS. 


(37,400  feet).  The  total  weight  of  the  gun  is  3  tons  (1,400 
kilograms  for  the  tube.  1.000  for  the  pun  carriage).  The  gun 
was  originally  constructed  for  use  on  a  field-L'iin  carriage.  Inn 
at  the  request  of  the  German  general  staff  the  Mercedes  work- 
shop succeeded  in  constructing  a  motor  truck  for  it  which  can 
easily  make  40  kilometers  (25  miles)  an  hour  on  good  roads. 
The  tires,  solid  front  and  rear,  with  a  diameter  of  1  meter, 
are  of  cast  steel.  The  car  is  equipped  with  a  G-cylinder  motor 


NO.   12.— KRUPP  75  MM.  L-35  FOR  AUTOMOBILE  MOUNT. 

developing  160  horsepower.  The  driver  is  the  only  man  on 
board.  The  ollicer  in  charge,  the  chief  gunner,  and  four  men 
follow  in  an  armored  car  capable  of  70  kilometers  (43  miles) 
an  hour  and  carrying  munitions,  as  well  as  an  armament  of  two 
machine  guns.  It  is  believed  that  this  gun  is  frequently  used 
on  a  fixed  mount  also. 

A   report  submitted   late  in  1010  states  that  in  order  to  pre- 
vent  hostile   aviators   from    Hying   low   enough   to   do   effective 


NOTES  ON  ANTI-AIRCRAFT  GUNS.  19 

work  with  their  machine  guns,  as  well  as  to  provide  for  the 
close  local  defense  of  balloons,  aviation  parks,  etc.,  the  Ger- 
mans have  been  installing  machine  cannon  of  37  millimeters 
(1^-inc'h)  caliber.  They  fire  a  solid  shot  with  a  smoke-tracing 
compound  in  the  base.  The  feeding  is  by  strips,  24  cartridges 
to  a  strip. 

Another  late  report  mentions  a  visit  to  two  German  anti- 
aircraft batteries  for  the  protection  of  Ostende  and  Zerbruegge, 
respectively.  Each  battery  consisted  of  four  4-inch  50-caliber 
guns  mounted  in  a  square  about  100  meters  on  the  side. 

One  late  report  also  gives  a  few  data  concerning  a  120-milli- 
meter (4.72-inch)  Krupp  anti-aircraft  coast  gun,  namely,  that 


NO.   13.— KRUPP  105  MM.  ON    MERCEDES  TRUCK. 

it  is  45  calibers  in  length  and  fires  a  24-kilogram  (53-pound) 
projectile  with  an  initial  velocity  of  800  meters  per  second 
(2,625  feet  per  second)  at  a  maximum  elevation  of  60°. 

Illustration  14  shows  an  unidentified  German  anti-aii-craft 
gun. 

Captured  75-millimeter  French  field  guns  in  improvised  bat- 
teries are  also  often  used  for  anti-aircraft  work.  To  secure 
the  high  elevation  necessary  either  the  wheels  are  set  on  a 
raised  center  pintle  with  a  circular  track  or,  the  wheels  remain- 
ing on  the  level  surface  of  the  ground,  a  circular  trench  is 
excavated  for  the  trail  of  the  gun  to  move  in. 


20 


NOTES  ON  ANTI-AIRCRAFT  GUNS. 


No.  14.— GERMAN  ANTI-AIRCRAFT  GUN. 

The  following  table,  though  its  data  can  not  in  general  be 
brought  into  relation  with  those  compiled  above,  is  added  be- 
cause very  recently  received : 


Type  and  caliber. 

Initial 
veloc- 
ity. 

Projec- 
tile, 
weight. 

Maxi- 
mum 
eleva- 
tion. 

Range. 

Weight 
of  gun 
and  car- 
riage. 

Weight 
of  gun, 
car- 
riage, 
and 
limber. 

Muzzle 
energy. 

KBITPP. 

75  mm.  30  cal.  field  car- 
riage. 

Meters. 
510 

Kilo- 
grams. 
6.5 

65 

Meters. 

Kilo- 
grams. 
1,030 

Kilo- 
grams. 

Meter- 
tonx. 

71  mm.  30  cal.  on  auto- 

1 5,850 

mobile 

1      650 

5 

75 

6,500 

1,230< 

»7,100 

104  mm.  45  cal.  coast  gun 

800 

15.5 

60 

120  mm.  45  cal.  coast  gun 

800 

24 

60 

EIIRIIARDT. 

50  mm   30  cal  on  auto- 

/ 

5  3,  100 

mobile 

570 

1.25 

70 

3,720 

{ 

«2,800 

65  mm.  35  cal.  on  auto- 
mobile   

670 

4.1 

75 

7,900 

6,000 

93.73 

75  mm.  30  cal.  on  auto- 
mobile .  .  . 

500 

6.5 

70 

5,860 

6,300 

82.76 

105  mm.  32  cal 

605 

17 

70 

8  300 

( 

••6,«50 

75  mm.  32  cal.  field  car- 
riage 

550 

6  5 

70 

6,800 

1 

6  5,  900 
1,800 

100.10 

i  Without  men  and  ammunition.      »  With  shields.  6  With  trailer. 

>  With  men  and  ammunition,  «  Without  shields.      5  Without  trailer. 


NOTES  ON  ANTI-AIRCRAFT  GUNS.  21 

ENGLAND. 

Aerial  defense  in  the  English  Army  consists  of:  (1)  Fixed 
anti-aircraft  artillery;  (2)  mobile  anti-aircraft  artillery;  and 
(3)  aeronautical  units  (not  here  under  consideration). 

Various  types  of  anti-aircraft  guns  are  in  use.  Among  them 
are  some  4.7-inch  naval  guns,  some  75  mm.  French  guns,  and 
some  5-inch  breech-loading  rifles.  The  later  types  in  more  com- 
mon use  are  the  3-inch  13-pounder,  the  3.3-inch  18-pounder, 
and  finally  the  3-inch  15-pounder,  which  ultimately  is  to  replace 
them  all. 

The  converted  3-inch  13-pounder  is  the  former  horse  artillery 
gun,  with  breech  bored  to  take  a  longer  cartridge  (with  an 
18-pounder  charge)  giving  an  increased  muzzle  velocity  of 
;,bout  2,000  foot-seconds.  These  guns  are  equipped  with  the 
ordinary  field  artillery  hand-operated  breech  mechanism  and 
are  mounted  for  mobile  work  on  pedestals  built  up  on  auto- 
mobiles and  revolving  through  360°.  There  is  one  gun  to  each 
motor  truck.  These  motors  are  of  45  horsepower.  Their  sides 
are  dropped  and  their  wheels  blocked  when  in  use.  The  maxi- 
mum range  is  from  6,700  to  7,000  yards,  and  the  highest  eleva- 
tion is  75°.  Six  batteries  of  these  guns  of  six  guns  each  are 
used  in  the  London  area. 

The  18-pounder  is  the  service  18-pounder  field  gun  mounted 
for  anti-aircraft  service.  These  guns  also  have  the  hand- 
operated  breech  mechanism.  They  give  an  initial  velocity  of 
about  1,750  foot-seconds.  They  are  mounted  on  transportable 
platforms  (see  below).  Some  of  these  guns  have  been  relined 
and  the  bore  decreased  to  3  inches.  These  relined  18-pounders 
fire  a  13-pound  projectile  with  an  increased  velocity  of  approxi- 
mately 2,000  foot-seconds.  Some  of  these  relined  18-pounders 
are  mounted  on  automobiles.  The  anti-aircraft  guns  which 
are  on  automobiles  are  mounted  directly  over  the  rear  axle  of 
standard  3-ton  motor  trucks  provided  with  two  outriggers,  so 
as  to  permit  of  firing  across  the  truck.  The  rear  outrigger 
consists  of  a  telescoping  beam  capable  of  being  drawn  out 
about  4  feet  beyond  the  sides  of  the  truck.  At  its  outer  ends 
are  two  jackscrews  which  distribute  the  load  over  about  3 
square  feet  of  ground  by  bearing  upon  blocks  which  are  carried 
on  the  truck.  The  front  outrigger  just  behind  the  driver's 
seat  extends  out  only  sufficiently  to  permit  of  the  use  of  the 
jackscrews.  The  body  of  the  truck  is  provided  with  sideboards 


22  NOTES  ON  ANTI-AIRCRAFT  GUNS. 

which,  when  dropped  down,  extend  the  platform  about  20  inches 
on  each  side.  The  trucks  have  single  tires  in  front  and  double 
tires  in  rear  and  are  equipped  with  governors  limiting  the 
speed  to  approximately  IN  miles  an  hour.  They  carry  a  small 
amount  of  ammunition,  while  additional  ammunition  is  carried 
on  other  motor  trucks. 

The  latest  gun,  one  which  has  been  especially  developed  dur- 
ing the  war  for  anti-aircraft  work,  is  the  8- inch  15-pounder 
20  hundredweight  gun  on  a  pedestal  mount.  This  is  the  one 
gun  which  has  been  adopted  as  standard  for  the  service  and  is 
to  replace  all  others.  It  is  considered  the  best  gun  for  the  pur- 
pose and  it  is  reported  that  both  French  and  Italian  officers 
admit  its  superiority  to  any  yet  developed.  It  is  being  supplied 
to  all  anti-aircraft  stations  as  rapidly  as  possible.  It  was  built 
to  have  an  initial  velocity  of  about  '2. 7~>0  foot-seconds,  now 
reduced,  however,  to  2..">0  foot-seconds,  because  with  a  higher 
velocity  the  gun  wears  out  too  rapidly.  The  gun  is  45  calibers 
long  and  has  a  height  range  of  2.~>.<H)0  feet.  The  gun  had  origi- 
nally semi-automatic  action  including  (1)  on  recoil,  unlocking 
and  opening  of  breechblock  and  ejection  of  shell  case;  (2)  on 
loading,  closing  and  locking  of  breechblock,  thereby  giving  a 
rate  of  fire  of  22  rounds  per  minute.  Owing  to  difficulties  ex- 
perienced at  the  higher  elevations  in  the  operation  of  the  semi- 
automatic mechanism,  the  standard  Tickers  type,  straight-pull 
breech  mechanism  (rate  of  fire  20  rounds  per  minute)  has  been 
used  instead.  The  gun  has  two  recoil  cylinders  with  springs  and 
piston.  The  recoil  is  only  11  inches.  The  traversing  and  ele- 
vating mechanism  are  each  of  the  rack  and  pinion  type,  tin- 
latter  with  worm  gear  to  prevent  running  down.  Two  telescopic 
sights  are  used,  one  on  the  right  for  deflection  and  one  on  the 
left  for  elevation,  so  mounted  and  controlled  that  all  corrections 
made  are  applied  to  both  telescopes.  Each  telescope  has  in- 
terior illumination  for  night  work  by  means  of  an  electric-light 
bulb.  It  can  be  fired  at  an  elevation  of  full  90°.  The  ammu- 
nition is  fixed,  and  after  the  present  supply  of  shrapnel  has 
been  exhausted,  high-explosive  shells  are  to  be  used  exclusively. 
It  is  the  intention  eventually  to  supply  guns  with  60  per  cent 
time  II.  E.  and  40  per  cent  percussion  H.  E.  fuses. 

The  15-pounder  20-huudredweight  guns  and  carriages  (also 
some  18-pounders)  are  mounted  on  a  transportable  platform  or 
ailtotrailers  of  structural  steel  .">  feet  square  and  IS  inches  deep. 
Four  arms  about  4  feet  in  length  are  hinged  at  the  corners  so 


NOTES  ON  ANTI-AIRCRAFT  GUNS. 


23 


that  they  can  be  swung  to  the  firing  position  on  the  diagonals 
of  the  platform  and  locked  by  pins  through  the  platform,  which 
is  thus  extended  sufficiently  to  give  the  gun  stability.  On  the 
bottom  of  the  platform  and  on  each  of  these  arms  are  angles 
approximately  3  by  3  inches,  which  by  engaging  the  surface  of 
the  ground  prevent  lateral  movement.  At  the  end  of  each  arm 
is  a  jackscrew.  To  go  into  action  the  trailer  is  detached  from 
the  motor  car,  the  arms  swung  out  and  locked,  and  the  jack- 
screws  run  down  until  the  weight  is  taken  off  the  two  wheels  of 


No.  15.— BRITISH  ANTI-AIRCRAFT  QUNS  ON  THE  WESTERN  FRONT. 

the  trailer.  As  the  wheel  axle  is  jointed  in  the  middle  and  held 
together  by  a  latch,  this  latch  is  now  released  and  the  two 
wheels  being  then  withdrawn,  the  jackscrews  are  run  out 
until  the  platform  rests  on  the  ground  ready  for  firing.  It  takes 
jx  trained  crew  only  about  one  minute  to  place  the  gun  in  action. 
The  gun  crew  consists  of  11  men. 

The  15-pounder  guns,  with  some  18-pounders,  mounted  on 
trailers  are  used  in  anti-aircraft  defenses  in  England  (84  of  the 
former  are  eventually  to  be  provided  for  the  aerial  defense  of 
London)  for  the  protection  of  ammunition  stores,  bases,  etc., 
and  behind  the  firing  line  in  France.  The  guns  mounted  on 
motor  trucks  (13-pounders  and  some  18-pounders)  are  used  im- 


24  NOTES  ON  ANTI-AIRCRAFT  GTJNS. 

mediately  behind  the  front  line  trenches  and  also  for  reinforcing 
the  anti-aircraft  fire  wherever  necessary. 


No.  16.— BRITISH  ANTI-AIRCRAFT  GUN  AT  SALONIKI. 

Illustration  15  shows  a  British  anti-aircraft  gun  on  the  west- 
ern front,  and  illustration  No.  16  one  at  Salonica. 

UNITED   STATES. 

The  only  weapon  designed  for  use  by  our  Army  specifically 
against  aircraft  is  a  3-inch  15-pounder,  having  the  same  con- 
struction and  ballistics  as  the  3-inch  15-pounder  model  of  1903. 
This  piece  will  be  equipped,  however,  with  a  semiautomatic 
breech  mechanism  and  a  drop  block.  The  carriage  provides  for 
firing  the  gun  at  elevations  between  0°  and  80°.  It  is  antici- 
pated that  a  maximum  altitude  of  about  30,000  feet  can  be 
obtained  with  this  gun  when  using  a  projectile  with  a  7-caliber 
ogive  and  a  muzzle  velocity  of  2,600  feet  per  second. 

The  Ordnance  Department  is  designing  or  building  three  dif- 
ferent types  of  mounts  for  anti-aircraft  artillery.  The  first  is  a 
fixed  pedestal  mount  for  the  3-inch  15-pounder  gun ;  the  other 


NOTES  ON  ANTI-AIRCRAFT  GUNS.  25 

two  mounts  are  for  a  3-inch  field  gun,  model  of  1902,  one  to  be 
emplaced  on  an  automobile  truck,  the  other  on  a  semiportable 
platform.  All  mounts  will  permit  a  maximum  elevation  of  85°. 
The  minimum  elevation  of  the  automobile  mount  will  be  35°, 
while  that  for  the  semifixed  and  3-inch  15-pounder  mounts  will 
be  12°  and  0°,  respectively. 

It  is  understood  that  the  Engineer  Department  has  plans  for 
mounting  the  standard  3-inch  antiaircraft  gun  and  carriage  as 
follows : 

(a)  On  a  standard  railway  flat  car  of  80,000  pounds  capacity, 
equipped  with  outriggers  which  will  enable  the  gun  to  be  fired 
from  the  car  at  any  point  by  blocking  up  under  the  ends  of  the 
outriggers. 

( I) )  On  a  light  flat  car  running  on  light  standard  gauge,  which 
can  be  pushed,  if  necessary,  from  point  to  point  and  which  can 
be  quickly  anchored  to  a  concrete  platform  to  be  constructed  in 
advance  and  laid  flush  with  the  ground  under  the  track  at 
points  where  it  is  desired  to  bring  the  gun  into  action,  the  gun 
to  be  fired  from  the  car  after  it  is  anchored  to  the  platform. 

(c)  On  a  truck  from  which  the  gun  can  be  fired  in  the  same 
manner  as  explained  under  (b),  but  which  can  be  hauled  over 
ordinary  roads  by  teams  or  automobile  tractors. 

The  methods  outlined  above  are  considered  by  the  Engineer 
Department  to  be  the  cheapest  and  most  practicable  for  the 
mobile  use  of  the  standard  3-inch  anti-aircraft  gun  and  car- 
riage. By  making  use  of  concrete  platforms  for  anchorages 
which  are  laid  flush  with  the  ground,  a  practically  level  base 
for  the  gun  when  fixed  is  secured  and  the  platform  can  be 
concealed  by  an  earth  covering  when  not  in  use.  It  is  also 
practicable  to  make  provisions  for  bolting  the  gun  pedestals 
directly  to  the  concrete  platforms  if  desired. 

The  new  Navy  anti-aircraft  gun,  developed  .after  three  years 
of  experiment,  is  a  machine  rifle  about  50  calibers  long  and 
capable  of  hurling  a  3-inch  shell  27,000  feet  into  the  air  at  an 
angle  of  90°,  and  can  deliver  its  charge  at  rapid-fire  rate. 

CONCLUSIONS. 

The  aeroplane  has  been  steadily  forced  to  higher  altitudes, 
and  to  counteract  this  the  anti-aircraft  gun  has  shown  a  corre- 
sponding tendency  to  increase  in  size,  power,  and  range.  The 


26  NOTES  ON  ANTI-AIRCRAFT  GUNS. 

size  of  aerial  defense  trims  used  in  the  present  war  has  ranged 
from  machine  guns  to  those  (if  4.  ."».  and  (>  indies  in  caliber. 

Aircraft  are  comparatively  safe  from  machine-gun  lire  at 
altitudes  greater  than  ,S,.~i<M)  feet.  For  anti-aircraft  work  the 
machine  guns,  like  the  rifles,  lack  range  and  also  effectiveness 
and  facilities  for  observation,  while  field  guns  do  not  possess 
sufficient  elevation  to  allow  of  their  being  trained  on  aircraft. 
nor,  were  they  once  trained  OB  a  so-rapidly  moving  target. 
would  they  be  able  to  follow  it. 

The  larger  the  caliber  the  better  (always  provided  the  requi- 
site rapidity  of  fire  can  be  secured)  in  order  to  compel  the 
enemy  to  fly  too  high  for  good  observation.  Anti-aircraft  guns 
on  mobile  mounts  should  have  a  caliber  of  not  less  than  3-inch, 
while  for  the  really  adequate  defense  of  any  important  position 
some  4-inch  guns  should  be  included.  If  the  guns  are  to  be 
in  fixed  emplacements,  their  caliber  should  be  6-inch. 

The  anti-aircraft  gun  must  have  a  high  muzzle  velocity,  so  as 
to  obtain  a  flat  trajectory.  To  secure  the  great  rapidity  'of  fire 
necessary  it  should  have  a  small  recoil  and  semiautomatic  load- 
ing. The  mounting  should  be  such  as  to  permit  the  greatest 
possible  elevation  (at  least  70°)  and  quick  traversing  over  the 
widest  possible  arc  of  fire,  preferably  360°.  It  should  be  easy  to 
sight  and  fire  rapidly  at  high  elevations.  If  suitable  in  other 
respects  an  ordinary  fieldpiece  can  be  used  against  aircraft  on 
almost  any  kind  of  improvised  mounting,  which  permits  great 
elevations  and  all-around  fire.  Such  mounts  are  makeshifts  at 
best,  however,  as  the  gunnery  will  necessarily  be  unsatisfactory. 

Tntil  recently  shrapnel  was  used  almost  exclusively  against 
aircraft,  but  as  experience  during  the  war  has  shown  shrapnel 
is  almost  useless  against  aeroplanes.  High  explosive  shells  are 
much  more  effective.  A  Farman  biplane  with  its  engine  worn 
out  from  use,  but  otherwise  practically  undamaged,  though  with 
over  400  shrapnel  and  bullet  holes,  has  been  exhibited  in  Paris. 

Mountings  for  anti-aircraft  guns  are  either:  (1)  Fixed  (in 
permanent  emplacements)  ;  (2)  transportable  (either  on  rail- 
way cars  with  outriggers,  on  flat  cars,  or  on  auto  trailers — the 
car  or  trailer  is  then  either  blocked  up  or  anchored  to  a  plat- 
form previously  prepared)  ;  (3)  mobile  (on  motor  trucks, 
armored  or  unarmored). 

Fixed  mountings  for  anti-aircraft  guns,  however  efficient, 
have  the  great  disadvantage  that  their  location  soon  becomes 
known  to  the  enemy.  Mobile  mountings,  on  the  other  hand, 


NOTES  ON  ANTI-AIRCRAFT  GUNS.  27 

greatly  enhance  the  value  of  anti-aircraft  guns.  They  permit  a 
more  effective  tactical  use  of  the  guns  by  introducing  into  air 
defense  the  very  important  element  of  surprise,  as  any  different 
number  of  positions  for  temporary  occupancy  may  be  selected 
without  previous  knowledge  of  the  enemy.  Also,  the  guns  can 
be  better  concealed.  The  principal  disadvantage  of  mobile 
mounts  is  in  the  instability  of  the  gun  platform  and  the  diffi- 
culty of  keeping  it  always  perfectly  level.  As.  however,  anti- 
aircraft guns  on  mobile  mounts  are  in  successful  use  by  both 
sides  abroad  it  is  evident  that  this  disadvantage  has  been  over- 
come. 

As  the  enemy  aeroplane  gets  beyond  range  very  quickly,  there 
is  no  time  for  elaborate  computations,  and  the  use  of  tables 
should  also  be  rendered  unnecessary.  The  gun  must  go  into 
action  at  once  and  maintain  an  extremely  rapid  fire  involving 
continual  changing  of  data  between  shots.  It  has  been  found 
best  to  fire  very  rapidly  with  as  many  guns  as  possible  and  try 
to  get  the  range  from  the  explosion  of  the  shell.  Anti-aircraft 
gunnery  is  thus  extremely  difficult,  and  gun  pointers  require 
careful  instruction  and  long  and  continuous  practice  to  attain 
any  degree  of  proficiency  and  avoid  waste  of  ammunition,  the 
expenditure  of  which  in  war  time  is  excessive.  At  best  anti- 
aircraft firing  is  very  inaccurate  and  volume  of  fire  must  be 
used  to  compensate  for  this  lack  of  accuracy.  The  tendency  is 
toward  simplification  in  all  sighting  apparatus  and  relying 
largely  on  correcting  fire  by  observation. 

Anti-aircraft  guns  should  accordingly  not  be  fired  singly. 
They  have  frequently  been  used  abroad  in  pairs  and  in  groups 
of  three  and  four.  The  tendency,  however,  is  toward  still 
larger  groups,  and  it  is  now  a  common  opinion  among  officers 
that  each  anti-aircraft  station  should  have  a  battery  of  not  less 
than  six  guns  in  order  to  secure  the  maximum  rapidity  of  fire, 
while  at  the  same  time  avoiding  some  of  the  errors  in  spotting 
by  establishing  a  zone  of  fire  around  the  hostile  aircraft.  As 
nearly  as  practicable  these  groups  of  guns  should  be  brought 
into  action  at  least  1,800  yards  apart.  All  gun  stations  should 
be  occupied  without  intermission  both  night  and  day,  and  it  is 
necessary  to  screen  the  guns  from  overhead  observation. 

Whereas  at  the  beginning  of  the  war  aeroplanes  flew  at  alti- 
tudes of  4,000  to  5,000  feet,  and  then  at  6,560  feet  (2.000 
meters),  with  comparative  safety,  the  so-called  safe  altitude 
has  been  gradually  increased,  first  to  10,000  feet  and  finally  to 


28  NOTES  ON  ANTI-AIRCRAFT  GUNS. 

12,000  feet  and  over  on  u  clear  day.  It  is  not  thought  probable 
that  artillery  attacks  against  aircraft  can  be  made  effective  for 
altitudes  of  15,000  feet  or  over,  though  an  occasional  bit  at  such 
an  altitude  even  may  occur.  Thus  in  October,  1916,  an  airman 
was  badly  wounded  by  a  high-explosive  shell  from  a  German 
gun  (presumably  the  10")  mm.  gun)  while  flying  at  the  great 
height  of  5,200  meters  (15,850  feet). 

Several  flyers  are  reported  to  have  been  brought  down  from 
a  height  of  4,000  meters  (13,120  feet).  Such  hits  are  very 
rare,  however.  The  speed  and  maneuvering  power  of  aero- 
planes make  them  extremely  difficult  targets  to  hit.  The  stead- 
ily increasing  altitudes  at  which  they  have  been  forced  to  fly 
adds  further  to  their  security,  but,  on  the  other  hand,  greatly 
diminishes  the  effectiveness  of  their  observations.  Thus  while 
pursuit  aeroplanes  now  fly  for  safety  at  about  18,000  feet,  the 
fighters  and  camera  machines  operate  between  10.000  and  12,000 
feet.  Now,  while  air  disturbances  due  to  the  bursting  of  a 
high-explosive  shell  :within  100  feet  of  an  aeroplane  might  cause 
[he  aeroplane  to  dtve  or  even  capsize,  it  would  not  necessarily 
wreck  the  machine;  therefore  a  direct  hit  on  some  vital  part 
of  the  aeroplane  is  necessary  to  bring  it  down.  As  above 
stated,  such  hits  are  rare,  but  the  anti-aircraft  gun  need  not 
hit  the  aeroplane  to  fulfill  its  function ;  if  it  can  force  the 
aeroplane  to  fly  too  high  for  good  observation  it  is  still  worth 
more  than  it  costs.  After  all,  however,  the  only  really  effective 
defense  against  hostile  aircraft  lies  in  an  aerial  service  of  our 
own  more  efficient  than  that  of  the  enemy.  For  this  purpose 
powerful  aeroplanes  equipped  with  machine  guns  or  light 
cannon  should  be  used. 

o 


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